"Calibrator" covers a wide range of instruments built for different jobs - a loop calibrator, a temperature/process calibrator, and a high-accuracy V/mA signal calibrator each solve a different problem, and picking the wrong one means either overpaying for accuracy you don't need or lacking the function you actually need. Vartech's calibrator range - the V 7220 R, V 7221 B and MS 7221 - covers all three.
V 7221 B - Loop Calibrator for 4-20 mA Circuits
A loop calibrator is built around one job: sourcing and measuring current in a 4-20 mA process control loop, the standard signal used by transmitters and controllers throughout industrial process plants. The V 7221 B sources DC current from 0-30 mA and simultaneously measures DC mA (±35 mA) and DCV (±35 V), with a 5-digit backlit display. Beyond simple DC step output, it also generates Sawtooth and Triangle wave signals - specifically useful for valve stroke testing (driving a control valve through its full travel to verify smooth response) and transmitter simulation. Span mode, on/off detection, torch and input protection (100 mA/250 V fast fuse) round it out for field commissioning and loop troubleshooting work.
V 7220 R - Temperature & Process Calibrator
The V 7220 R covers a broader measurement scope than a pure loop calibrator: it can source and measure DCV, resistance, thermocouple signals across multiple T/C types, and RTD signals in 2-wire, 3-wire and 4-wire configurations. This is the instrument for calibrating temperature transmitters, RTD sensors and thermocouple-based instrumentation - anywhere the signal being tested is a temperature measurement rather than a generic 4-20 mA process value. Its 5-digit backlit display and built-in torch suit field calibration work in plant environments.
Choosing between them
MS 7221 - High-Accuracy V/mA Process Signal Calibrator
The MS 7221 is built for a narrower but higher-precision job: sourcing and measuring DC loop current (0-24 mA) and DC voltage (0-100 mV or 0-10 V) with accuracy of ±(0.015% + 4 digits) on current and ±(0.02% + 2 digits) on voltage - meaningfully tighter than a general-purpose loop calibrator. Its built-in 24 V loop supply powers a 2-wire transmitter directly while simultaneously measuring its output current, eliminating the need for a separate power source during calibration. This is the instrument for instrumentation workshops and process plant maintenance where calibration accuracy itself is being verified or audited, not just functional loop testing.
Quick Reference
- 4-20 mA loop testing, valve stroke and transmitter simulation: V 7221 B loop calibrator.
- Thermocouple/RTD sensor and temperature transmitter calibration: V 7220 R temperature & process calibrator.
- High-accuracy 2-wire transmitter calibration with loop power built in: MS 7221.
- General process instrumentation, unsure which function you need: see our general process calibrator guide or contact us.
CIE Instruments is an authorised distributor for the full Vartech calibrator range - the V 7221 B, V 7220 R and MS 7221. Contact us with your measurement and accuracy requirement for a recommendation.